chickadee » random-access-lists » ral-join

function (result)
requires (and (ral? head) (ral? tail)
              (eq? (ral-item? head) (ral-item? tail)))
ensures  (and (ral? result)
              (fx= (ral-count result)
                   (fx+ (ral-count head) (ral-count tail))))